Flat-panel display devices are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a substrate to display images. Each pixel incorporates several, differently colored light-emitting elements commonly referred to as sub-pixels, typically emitting red, green, and blue light, to represent each image element. Pixels and sub-pixels are not distinguished herein; all light-emitting elements are called pixels. A variety of flat-panel display technologies are known, for example plasma displays, liquid crystal displays, and light-emitting diode displays. Active-matrix elements are not necessarily limited to displays and can be distributed over a substrate and employed in other applications requiring spatially distributed control.
Area light-emitting diodes (LEDs) incorporating thin films of light-emitting materials forming light-emitting elements have many advantages in a flat-panel display device and are useful in optical systems. Organic LED color displays that include an array of organic LED light-emitting elements are known. Alternatively, inorganic materials can be employed and can include phosphorescent crystals or quantum dots in a polycrystalline semiconductor matrix. Other thin films of organic or inorganic materials can also be employed to control charge injection, transport, or blocking to the light-emitting-thin-film materials, and are known in the art. The materials are placed upon a substrate between electrodes, with an encapsulating cover layer or plate. Light is emitted from a pixel when current passes through the light-emitting material. The frequency of the emitted light is dependent on the nature of the material used. In such a display, light can be emitted through the substrate (a bottom emitter) or through the encapsulating cover (a top emitter), or both.
LED devices can include a patterned light-emissive layer wherein different materials are employed in the pattern to emit different colors of light when current passes through the materials. Alternatively, one can employ a single emissive layer, for example, a white-light emitter, together with color filters for forming a full-color display. It is also known to employ a white sub-pixel that does not include a color filter, or to employ an un-patterned white emitter with a four-color pixel comprising red, green, and blue color filters and sub-pixels and an unfiltered white sub-pixel to improve the efficiency of the device.
Two different methods for controlling the pixels in a flat-panel display device are generally known: active-matrix control and passive-matrix control. In an active-matrix device, control elements are distributed over the flat-panel substrate. Typically, each sub-pixel is controlled by one control element and each control element includes at least one transistor. For example, in a simple active-matrix organic light-emitting (OLED) display, each control element includes two transistors (a select transistor and a power transistor) and one capacitor for storing a charge specifying the brightness of the sub-pixel. Each light-emitting element typically employs an independent control electrode and a common electrode.
Prior-art active-matrix control elements typically include thin-film semiconductor materials, such as silicon, formed into transistors and capacitors through photolithographic processes. The thin-film silicon can be either amorphous or polycrystalline. Thin-film transistors made from amorphous or polycrystalline silicon are relatively larger and have lower performance than conventional transistors made from crystalline silicon wafers. Moreover, such thin-film devices typically exhibit local or large-area non-uniformity that results in perceptible non-uniformity in a display employing such materials, and the manufacturing processes are expensive.
Matsumura et al discuss crystalline silicon substrates used with LCD displays in US 2006/0055864. Matsumura describes a method for selectively transferring and affixing pixel-control devices made from first semiconductor substrates onto a second planar display substrate. Wiring interconnections within the pixel-control device and connections from busses and control electrodes to the pixel-control device are shown.
Regardless of the control methodology for a flat-panel display device, active-matrix display devices incorporate control elements within the flat panel for controlling the individual pixels. These control elements receive data from a display controller external to the display. The data is communicated via electrical signals transmitted through wires formed on the flat-panel display substrate. Such control signals are limited in bandwidth because of the length of the wires, the wire conductivity, and the arrangement of the wires. For large displays of high resolution, such communication bandwidth restrictions can limit the refresh rate of the display, the resolution, or the accuracy and precision of the display signals.
Optical communication on a circuit board is described in U.S. Pat. Nos. 7,095,620 and 7,120,327. A photonic interconnection system is described in U.S. Pat. No. 7,546,004. A computer system with optical buss architecture is described in US 2002/0178319. However, these disclosures do not provide improved communication between pixel control elements in a flat-panel display.
U.S. Pat. No. 5,200,631 describes communication between chips on stacked substrates, e.g., circuit boards plugged into a backplane. US 2009/0289265 describes a similar scheme, only for vertically-stacked dice in a multi-chip system-in-package. These schemes are not applicable to display devices, in which the substrate viewed by the user cannot be obscured by a stacked substrate or other component.
US 2010/0001639 describes an optical touchscreen using an OLED. Light emitted by the OLED reflects off an object pressed against the screen and is detected by an on-panel photosensor. This scheme does not provide communication between active-matrix control elements, and depends on objects external to the display to reflect light.
WO2010046643 describes chiplets including light sensors for detecting the position of the chiplet and OLED with respect to each other. It does not address the need to improve communication between active-matrix control elements.
There is a need, therefore, for an improved method of communicating signals to and between active-matrix elements in a flat-panel display.